The present invention relates to the operation of laser scanners, and in particular to an apparatus for simultaneously generating both a pointer beam and scan pattern from a single laser source.
Bar code scanners are used in a wide range of retail, commercial, and industrial applications to read bar code symbols on numerous items for purposes such as check-out, inventory and tracking. Laser scanners developed for such applications include fixed scanners, such as counter-top scanners for check-out applications, and hand held scanners, which are used for many inventory and tracking applications. Typically, fixed scanners generate a scan pattern having a plurality of scan lines configured to provide a degree of freedom from orientation and directional constraints for bar code labels moving through the scan volume. By contrast, hand-held scanners typically use a single scan line pattern to read bar code symbols and, of course, rely on manual manipulation of the scanner to find the bar codes.
Representative of prior art laser scanners are compact scanners disclosed by Hellekson et al in U.S. Pat. No. 4,861,973 (the '973 patent), issued Au. 29, 1989; and hand-held laser scanners disclosed by Lonsdale et al, U.S. Pat. No. 4,678,288 (the '288 patent), issued Jul. 7, 1987. Regardless of the embodiment, laser scanners have an optical system composed of transmission optics, collection optics and a scan pattern generating arrangement.
The transmission optics typically include a low power laser, one or more small routing mirrors, a diverging lens, which may be on the end of the laser, and a focusing lens, which may be molded as part of a larger collection lens of the collection optics. The basic function of the transmission optics is to create and transmit a beam of laser light of the correct diameter to the scan pattern generating arrangement, which further transmits either a laser beam at the plane of the package label to illuminate the bars and spaces of a bar code symbol on the label. The scan pattern generating arrangement causes the beam to sweep across the package label in one or more scan lines.
The collection optics typically include a collection lens, a bandpass filter and a photodetector. The basic function of the collection optics is to gather and collect only the diffuse laser light reflected from the label and focus it onto a small detector. The light is collected and focused in such a way as to optimize the signal-to-noise ratio. In a retro-directive optical system, a cone of light returning from the label and surrounding the beam of light being transmitted to the label is collected by the collection lens. In this way, a substantial portion of ambient light is eliminated from the system. Additional filtering of ambient light "noise" is achieved by the bandpass filter.
The scan pattern generating arrangements of prior art laser scanners vary greatly. In a typical counter-top scanner they employ an optical arrangement including a mirror assembly consisting of a plurality of primary reflective mirror surfaces which spin about an axis, and further include a multiplicity of secondary reflective elements which move the beam of laser light through a three dimensional pattern capable of finding and reading labels in as many orientations as possible. Typical hand-held scanners may employ a similar arrangement including a spinning or rotating device to generate one or more scan lines. Hand-held scanners may also employ a simpler arrangement where an optical element, such as a mirror, alternately rotates through an arc in different directions, i.e. reciprocates, to generate a single scan line, as in the '288 patent. Such alternate rotation in an arc or reciprocation, typically in small amplitude motions, is referred to herein as dithering.
A problem arises where laser scanners, in particular hand-held scanners, are used to scan bar code labels located a great distance from the laser scanner. Over distances of several feet scan lines become so diffuse that they are not readily visible on a target, making it difficult to properly aim the scanner at the target or effectively manipulate the target to be read. This is because the path of the beam across the surface carrying the bar code label is not visible to the operator of the scanner due to the high speed of movement of the beam tracing the scan line. Thus, for example, it has been found that targeting and reading a bar code 3 inches by 1 inch in size at a distance of five feet becomes problematic.
In response to this problem laser scanners have been developed having a two-position trigger which causes the laser scanner to generate either a scan line or a fixed pointer beam for aiming the laser scanner. The fixed pointer beam is visible over a greater distance, because the light energy is concentrated in a spot. However, the two-position scanners have the disadvantage of requiring manual switching of the scanner between operating modes and, once switched from the pointing mode back to the scanning mode, they again leave the operator "blind" to the direction in which the scanner is pointed while scanning.
Accordingly, further improvements in performance and improved targeting capability are desired to satisfy the continuing need for high performance scanners used in a wide range of applications.